I am preparing polycrystalline diamond (PCD) with tape casting. The powder is 8~12 um.
After drying of tapes, I place several tapes in Ta cup without warm-pressing. Next, debinding is carried out. There are no cracks visible with naked eye. SEM analysis shows all the organics are evaporated.
After debinding, WC-Co substrate (4 um average particle size of WC) is placed in cup over debinded tapes. Heat treatment is done in vacuum above 1000 C for surface graphitization to help in sintering.
After that, high pressure high temperature sintering is carried out. When surface is observed after polishing, there are whitish parts on the dark gray diamond surface, mostly in circles. These discolored parts are mostly near the edge of sample, and sometimes inwards too, for example, in the center of a sample. Sometimes, these discolors are distributed throughout the sample.
What may the reason of these discolors?
Additionally, mostly there are also cracks near the edge of sample. What could be the reason for these cracks?
Hi Sir,
From my perspective, if the whitish discoloration occurs, it should be due to one of the following reasons:
Oxidation: the presence of oxides on the surface can lead to a whitish appearance.
Presence of fouling factors: any residuals that remain on the surface after removal can cause discoloration.
Improper mix of materials: sometimes, an improper mix of materials (in powder form) used for sintering may lead to discoloration.
Regarding the cracks, I believe they may be due to thermal or mechanical stress, or possibly an improper mix of materials.
My suggestion is to try to control the heat treatment process by starting it very slowly to minimize these stresses.
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